Propylene copolymers grafted using free radical initiators

ABSTRACT

Propylene copolymers grafted with α,β-ethylenically unsaturated carboxylic acids or carboxylic acid derivatives and consisting of 
     a 1 ) a random propylene copolymer (A 1 ) containing from 0.1 to 15% by weight of polymerized C 2  -C 10  -alk-1-enes or of 
     a 2 ) a propylene copolymer (A 2 ) comprising a random propylene copolymer (I) containing from 0.1 to 15% by weight of polymerized C 2  -C 10  -alk-1-enes and a random propylene copolymer (II) containing from 15 to 80% by weight of polymerized C 2  -C 10  -alk-1-enes or of 
     a 3 ) a propylene copolymer (A 3 ) comprising a propylene homopolymer (III) and a random propylene copolymer (IV) containing from 15 to 80% by weight of polymerized C 2  -C 10  -alk-1-enes, 
     are obtainable by reacting the monomer to be grafted with the propylene copolymer (A 1 ), (A 2 ) or (A 3 ) at from 1 to 300 bar, from 0.01 to 1.0% by weight of the monomer to be grafted, where both stated concentrations are based on the propylene copolymer, being added to the molten propylene copolymer in the presence of from 0.005 to 0.5% by weight of a free radical initiator and the grafting reaction being carried out at from 200° to 350° C.

The present invention relates to propylene copolymers grafted withα,β-ethylenically unsaturated carboxylic acids or carboxylic acidderivatives and consisting of

a₁) a random propylene copolymer (A₁) containing from 0.1 to 15% byweight of polymerized C₂ -C₁₀ -alk-1-enes or of

a₂) a propylene copolymer (A₂) comprising a random propylene copolymer(I) containing from 0.1 to 15% by weight of polymerized C₂ -C₁₀-alk-1-enes and a random propylene copolymer (II) containing from 15 to80% by weight of polymerized C₂ -C₁₀ -alk-1-enes

or of

a₃) a propylene copolymer (A₃) comprising a propylene homopolymer (III)and a random propylene copolymer (IV) containing from 15 to 80% byweight of polymerized C₂ -C₁₀ -alk-1-enes,

obtainable by reacting the monomer to be grafted with the propylenecopolymer (A₁), (A₂) or (A₃) at from 1 to 300 bar, from 0.01 to 1.0% byweight of the monomer to be grafted, where both stated concentrationsare based on the propylene copolymer, being added to the moltenpropylene copolymer in the presence of from 0.005 to 0.5% by weight of afree radical initiator and the grafting reaction being carried out atfrom 200° to 350° C.

The present invention furthermore relates to a process for thepreparation of these grafted propylene copolymers and a process for thepreparation of crosslinked or crosslinkable propylene copolymers and tothe use of the grafted propylene copolymers as adhesion promoters,films, fibers or moldings.

Graft copolymers can be prepared by first reacting the polymer to begrafted with peroxides and then bringing the product into contact withsuitable monomers (U.S. Pat. No. 3,862,265, U.S. Pat. No. 3,953,655 andU.S. Pat. No. 4,001,172). The treatment with the peroxides acting asinitiators results initially in the formation of free radicals on thepolymer chain, with which radicals monomers can undergo an additionreaction in the subsequent grafting reaction.

Processes in which homo- or copolymers of ethylene are first graftedwith unsaturated carboxylic acids and/or esters or anhydrides thereof bya reaction initiated by organic peroxides and then reacted withpolyfunctional amines or alcohols are also known (DE-A 2 627 785, EP-A50 994, U.S. Pat. No. 4,089,794, U.S. Pat. No. 4,137,185, U.S. Pat. No.4,161,452, U.S. Pat. No. 4,382,128). Crosslinked products which are verystable but, owing to their poor melt flow, cannot be processed thermallyby the methods conventionally used in plastics technology are generallyformed.

Processes for the preparation of grafted or crosslinked polypropyleneshave also been described, but some of the processes have considerabledeficiencies. For example, in grafting or crosslinking reactions, theuse of peroxides generally leads to a decrease in the molecular weight,which causes the mechanical properties of the product obtainable todeteriorate to a substantial extent [J. Appl. Poly. Sci., 32 (1986),5431-5437]. In another possible method of crosslinking polypropylenes,the latter are first grafted with vinylsilanes and then crosslinked bycondensation with steam using an organic tin catalyst (DE-A 3 520 106,U.S. Pat. No. 3,328,339). However, this process is very expensive sincethe generally toxic tin catalysts can be removed from the product onlywith difficulty. Moreover, all silane groups required for adhesion ofthe polymer melt to polar substrates are hydrolyzed by water on cooling,making it virtually impossible to produce multilayer composites. FrenchPatent 2,572,417 furthermore discloses a process in which polypropylenecan be grafted by reaction with organic peroxides and unsaturatedcarboxylic anhydrides.

On the basis of the prior art, there are certain reservations about theuse of free radical initiators, for example peroxides, in graftingreactions. For example, it is known that the use of high peroxideconcentrations in the grafting of polypropylenes leads as a rule to asharp decrease in molecular weight and to a reduction in the adhesion topolar substances, for example metals or polyamides, so that theresulting polymer does not have satisfactory performancecharacteristics.

DE-A 4 022 570 discloses the preparation of grafted propylene copolymersin the absence of free radical initiators. This process, which is easyto carry out, gives graft copolymers which have good mechanicalproperties and may furthermore be converted with crosslinking agentsinto crosslinked or crosslinkable materials.

However, the disadvantage of the process described in DE-A 40 22 570 isthat the propylene copolymers obtained therefrom frequently do notexhibit very high grafting yields, which is important for certainapplications. The grafting yield is understood as meaning the percentageof grafted monomers, based on the total amount of graft monomers used.The not very high grafting yields result in adhesive strengths andtensile strengths, relative to materials such as glass, polyamide ormetals, which are unsatisfactory for certain applications.

It is an object of the present invention to remedy the disadvantagesdescribed and to provide grafted propylene copolymers which exhibit ahigh grafting yield and improved tensile strength.

We have found that this object is achieved by the propylene copolymersdefined at the outset and grafted with ethylenically unsaturatedcarboxylic acids or carboxylic acid derivatives.

α,β-unsaturated carboxylic acids or carboxylic acid derivatives are usedas graft monomers in the process leading to the novel propylenecopolymers. α,β-unsaturated carboxylic acids or carboxylic acidderivatives are to be understood as meaning the conventional carboxylicacids copolymerizable with propylene, and the ester, anhydride or amidederivatives thereof. Maleic acid, fumaric acid, itaconic acid, acrylicacid, crotonic acid or anhydrides thereof are among the substancespreferably used, maleic anhydride being particularly suitable.

In the process leading to the novel propylene copolymers, the monomer tobe grafted is reacted with a propylene copolymer which consists of

a₁) a random propylene copolymer (A₁) containing from 0.1 to 15% byweight of polymerized C₂ -C₁₀ -alk-1-enes

or of

a₂ ) a propylene copolymer (A₂) comprising

a random propylene copolymer (I) containing from 0.1 to 15% by weight ofpolymerized C₂ -C₁₀ -alk-1-enes and

a random propylene copolymer (II) containing from 15 to 80% by weight ofpolymerized C₂ -C₁₀ -alk-1-enes

or of

a₃) a propylene copolymer (A₃) comprising a propylene homopolymer (III)and a random propylene copolymer (IV) containing from 15 to 80% byweight of polymerized C₂ -C₁₀ -alk-1-enes.

If a random propylene copolymer (A₁) is used as the propylene copolymer,preferred random propylene copolymers are those in which the content ofcomonomers is from 0.2 to 12, in particular from 0.3 to 9, % by weight.In particular, ethylene, but-1-ene, pent-1-ene, hex-1-ene, hept-1-ene oroct-1-ene is used as C₂ -C₁₀ -alk-1-ene, and, in the preparation ofthese copolymers, the C₂ -C₁₀ -alk-1-enes may be copolymerized eitherindividually or as mixtures together with the propylene.

The novel grafted propylene copolymers may also contain the propylenecopolymer (A₂). A propylene copolymer (A₂) which comprises a randompropylene copolymer (I) containing from 0.2 to 12, in particular from0.3 to 9, % by weight of polymerized C₂ -C₁₀ -alk-1-enes and a randompropylene copolymer (II) containing from 20 to 75, in particular from 25to 70, % by weight of polymerized C₂ -C₁₀ -alk-1-enes is preferablyused. In particular, ethylene, but-1-ene, pent-1-ene, hex-1-ene,hept-1-ene or oct-1-ene is used as the C₂ -C₁₀ -alk-1-ene, and, in thepreparation of these copolymers, the C₂ -C₁₀ -alk-1-enes may becopolymerized either individually or as mixtures together with thepropylene.

A preferably used propylene copolymer (A₂) is one which comprises from25 to 97% by weight of the random propylene copolymer (I) and from 3 to75% by weight of the random propylene copolymer (II). Particularlypreferred propylene copolymers (A₂) contain from 35 to 95, in particularfrom 40 to 93, % by weight of the random propylene copolymer (I) andfrom 5 to 65, in particular from 7 to 60, % by weight of the randompropylene copolymer (II).

The novel grafted propylene copolymers may furthermore contain thepropylene copolymer (A₃).

A preferably used propylene copolymer (A₃) is one whose random propylenecopolymer (IV) contains from 20 to 75, in particular from 25 to 70, % byweight of polymerized C₂ -C₁₀ -alk-1-enes. In particular, ethylene,but-1-ene, pent-1-ene, hex-1-ene, hept-1-ene or oct-1-ene is used as theC₂ -C₁₀ -alk-1-ene, and, in the preparation of these copolymers, the C₂-C₁₀ -alk-1-enes may be copolymerized either individually or as mixturestogether with the propylene.

A preferably used propylene copolymer (A₃) is one which consists of from25 to 97% by weight of the propylene homopolymer (III) and of from 3 to75% by weight of the random propylene copolymer (IV). Particularlypreferred propylene copolymers (A₃) contain from 30 to 95, in particularfrom 35 to 90, % by weight of the propylene homopolymer (III) and from 5to 70, in particular from 10 to 65, % by weight of the random propylenecopolymer (IV).

These propylene copolymers (A₁), (A₂) or (A₃) are usually prepared bypolymerization with the aid of Ziegler-Natta catalysts. These contain,inter alia, a titanium-containing solid component as well as acocatalyst. A suitable cocatalyst is an aluminum compound. In additionto this aluminum compound, an electron donor compound is preferably usedas a further component of the cocatalyst. The polymerization is carriedout in the reactors usually used in industry for polymerizationreactions, preferably in the gas phase.

For the preparation of the titanium-containing solid component, thetitanium compounds used are in general halides or alcoholates oftrivalent or tetravalent titanium, the chlorides of titanium, inparticular titanium tetrachloride, being preferred. Advantageously, thetitanium-containing solid component contains a finely divided carrier,silicas and aluminas as well as aluminum silicates of the empiricalformula SiO₂.aAl₂ O₃, where a is from 0.001 to 2, in particular from0.01 to 0.5, having proven useful for this purpose.

Compounds of magnesium are also among the substances used in thepreparation of the titanium-containing solid component. Particularlysuitable compounds of this type are magnesium halides, alkylmagnesiumsand arylmagnesiums, as well as alkoxymagnesium and aryloxymagnesiumcompounds, magnesium chloride, magnesium bromide and di-C₁ -C₁₀-alkylmagnesium compounds being preferably used. The titanium-containingsolid component may also contain halogen, preferably chlorine orbromine.

The titanium-containing solid component furthermore contains electrondonor compounds, for example monofunctional or polyfunctional carboxylicacids, carboxylic anhydrides and carboxylates, and ketones, ethers,alcohols, lactones and organophosphorus and organosilicon compounds.Preferably used electron donor compounds in the titanium-containingsolid component are phthalic acid derivatives of the general formula I##STR1## where X and Y are each chlorine or C₁ -C₁₀ -alkoxy or togetherare oxygen. Particularly preferred electron donor compounds arephthalates where X and Y are each C₁ -C₈ -alkoxy, for example methoxy,ethoxy, propoxy or butoxy.

Further preferred electron donor compounds in the titanium-containingsolid component include diesters of 3-membered or 4-membered,unsubstituted or substituted cycloalkane-1,2-dicarboxylic acids andmonoesters of unsubstituted or substituted benzophenone-2-carboxylicacids. The hydroxy compounds used in these esters are the alcoholsconventionally used in esterification reactions, including C₁ -C₁₅-alkanols, C₅ --C₇ -cycloalkanols, which in turn may carry C₁ -C₁₀-alkyl groups, and C₆ -C₁₀ -phenols.

The titanium-containing solid component may be prepared by methods knownper se. Examples of these are described in, inter alia, EP-A 45 975,EP-A 45 977, EP-A 86 473, EP-A 171 200, GB-A 2 111 066 and U.S. Pat. No.4,857,613.

The titanium-containing solid component obtainable in this manner isused with cocatalysts as a Ziegler-Natta catalyst system. Suitablecocatalysts are aluminum compounds and further electron donor compounds.

Aluminum compounds suitable as a cocatalyst are trialkylaluminum as wellas those compounds in which one alkyl group is replaced by an alkoxygroup or by a halogen atom, for example by chlorine or bromine.Trialkylaluminum compounds whose alkyl groups are each of 1 to 8 carbonatoms, for example trimethyl-, triethyl- or methyldiethylaluminum, arepreferably used.

In addition to the aluminum compound, electron donor compounds, forexample mono- or polyfunctional carboxylic acids, carboxylic anhydridesand carboxylates, or ketones, ethers, alcohols, lactones andorganophosphorus and organosilicon compounds, are also preferably usedas further cocatalyst. Preferred electron donor compounds areorganosilicon compounds of the general formula II

    R.sup.1.sub.n Si(OR.sup.2).sub.4-n                         II.

where

the radicals R¹ are identical or different and are each C₁ -C₂₀ -alkyl,a 5-membered to 7-membered cycloalkyl group which in turn may carry a C₁-C₁₀ -alkyl group, or C₆ -C₂₀ -aryl or arylalkyl, the radicals R² areidentical or different and are each C₁ -C₂₀ -alkyl and n is 1, 2 or 3.Particularly preferred compounds are those in which R¹ is C₁ -C₈ -alkylor a 5-membered to 7-membered cycloalkyl group, R² is C₁ -C₄ -alkyl andn is 1 or 2.

Among these compounds, dimethoxydiisopropylsilane,dimethoxyisobutylisopropylsilane, dimethoxydiisobutylsilane,dimethoxydicyclopentylsilane, diethoxyisobutylisopropylsilane anddimethoxyisopropyl-sec-butylsilane are particularly noteworthy.

Preferably used catalyst systems are those in which the atomic ratio ofaluminum from the aluminum compound to titanium from thetitanium-containing solid component is from 10:1 to 800:1, in particularfrom 20:1 to 200:1, and the molar ratio of the aluminum compound to theelectron donor compound used as the cocatalyst is from 1:1 to 100:1, inparticular from 2:1 to 80:1. The individual catalyst components may beintroduced into the polymerization system in any order, individually oras a mixture of two components.

With the aid of such catalyst systems, it is possible to prepare thepropylene copolymers (A₁), (A₂) or (A₃) required for the preparation ofthe novel, grafted polymers.

The random propylene copolymers (A₁) are preferably prepared bypolymerization of the propylene and of the C₂ -C₁₀ -alk-1-enes used ascomonomers in a reactor in the absence of a liquid reaction medium atfrom 20 to 40, in particular from 25 to 35, bar, at from 60° to 90° C.,in particular from 65° to 85° C. and during an average residence time ofthe polymer of from 0.5 to 5 hours. A process where the ratio of thepartial pressure of propylene to that of the C₂ -C₁₀ -alk-1-enes isbrought to 5:1-100:1, in particular 5:1-50:1, is preferred. The reactorsused may be the apparatuses conventionally employed in polymerizationtechnology. The molecular weight of the propylene copolymers (A₁) can beregulated by conventional regulators, for example hydrogen.

The propylene copolymers (A₂) are obtainable, inter alia, by firstpreparing the random propylene copolymer (I) in a first polymerizationstage and then adding to it the random propylene copolymer (II). Thismay be effected, for example, in a two-stage reactor cascade. The orderof the preparation of the individual propylene copolymers (I) and (II)may also be reversed.

The polymerization in the first polymerization stage is preferablycarried out at from 20 to 40, in particular from 25 to 35, bar, at from60° to 90° C., in particular from 65° to 85° C. and during an averageresidence time of the reaction mixture of from 0.5 to 5, in particularfrom 1.0 to 4, hours. Usually, the reaction conditions are chosen sothat, in the first polymerization stage, from 0.05 to 2 kg, preferablyfrom 0.1 to 1.5 kg, of the propylene copolymer (I) is/are formed permmol of the aluminum component. It is advisable to bring the ratio ofthe partial pressure of propylene to that of the C₂ -C₁₀ -alk-1-ene toabout 5:1-500:1, in particular 10:1-200:1. The polymerization may becarried out in the presence of regulators, for example of hydrogen.

The propylene copolymer (I) obtainable in this manner is dischargedtogether with the catalyst from the first polymerization stage after theend of the reaction and is introduced into the second polymerizationstage, where the propylene copolymer (II) is formed by polymerizationwith a mixture of propylene and further C₂ -C₁₀ -alk-1-enes.

In the second polymerization stage, the polymerization is preferablyeffected at from 5 to 30, in particular from 10 to 25, bar, at from 30°to 80° C., in particular from 40° to 70° C., and during an averageresidence time of from 0.5 to 5, in particular from 1.0 to 4, hours. Inthis case, the ratio of the partial pressure of propylene to that of theC₂ -C₁₀ -alk-1-ene is from about 0.1:1 to 20:1, in particular from0.15:1 to 15:1. The weight ratio of the monomers reacted in the firstpolymerization stage to that of the monomers reacted in the secondpolymerization stage is from about 33:1 to 1:3, in particular from 19:1to 1:2.

It may also be advisable to add a C₁ -C₈ -alkanol, in particular a C₁-C₄ -alkanol, to the reaction mixture of the second polymerizationstage, said alkanol influencing the activity of the Ziegler-Nattacatalyst. Alkanols suitable for this purpose include methanol, ethanol,n-propanol, n-butanol and very particularly isopropanol. The amount ofthe C₁ -C₈ -alkanol is advantageously such that the molar ratio of theC₁ -C₈ -alkanol to the aluminum compound serving as a cocatalyst is from0.01:1 to 10:1, in particular from 0.02:1 to 5:1.

The molecular weight of the propylene copolymers (II) obtainable can beregulated in the conventional manner by adding regulators, in particularhydrogen. Inert gases, such as nitrogen or argon, may also be present.

The propylene copolymer (A₂) to be used according to the invention andconsisting of the random propylene copolymer (I) and the randompropylene copolymer (II) is obtained in this manner.

The propylene copolymers (A₃) can advantageously be prepared by atwo-stage process in which propylene is polymerized in a firstpolymerization stage to give the propylene homopolymer (III), with whichthe propylene copolymer (IV) is then mixed in a second polymerizationstage by polymerization of a mixture of propylene and one or more C₂-C₁₀ -alk-1-enes.

The polymerization of the propylene in the first polymerization stage isusually carried out at from 20 to 40, preferably from 20 to 35, bar, andfrom 60° to 90° C., preferably from 65° to 85° C., and during an averageresidence time of the reaction mixture of from 0.5 to 5, preferably from1.0 to 4, hours. The reaction conditions are usually chosen so that, inthe first polymerization stage, from 0.05 to 2 kg, preferably from 0.1to 1.5 kg, of the propylene homopolymer (III) are formed per mmol of thealuminum component.

The propylene homopolymer (III) obtained is discharged with the catalystfrom the first polymerization stage after the end of the reaction and isintroduced into the second polymerization stage, where a mixture ofpropylene and one or more C₂ -C₁₀ -alk-1-enes, in particular ethylene orbut-1-ene, is polymerized with it. The pressure prevailing in the secondpolymerization stage is 7, preferably 10, bar below that of the firstpolymerization stage and is from 5 to 30, preferably from 10 to 25, bar.The temperature is from 30° to 100° C., preferably from 35° to 80° C.,and the average residence time of the polymer is from 0.5 to 5,preferably from 1.5 to 4, hours.

In the second polymerization stage, the ratio of the partial pressure ofpropylene to that of the C₂ -C₁₀ -alk-1-ene or C₂ -C₁₀ -alk-1-enes isusually from 0.1:1 to 10:1, in particular from 0.5:1 to 8:1. The weightratio of the monomers reacted in the first polymerization stage to themonomers reacted in the second polymerization stage is preferably from0.1:1 to 20:1, in particular from 0.2:1 to 15:1.

The novel, grafted propylene copolymers are preferably prepared by aprocess in which from 0.01 to 1.0% by weight, based on the propylenecopolymer, of the monomer to be grafted is mixed with the moltenpropylene copolymer (A₁), (A₂) or (A₃) at from 1 to 300, preferably from1 to 250, bar in the presence of a free radical initiator, and thegrafting reaction is carried out at from 200° to 350° C. The monomer tobe grafted is preferably used in concentrations of from 0.01 to 0.8, inparticular from 0.01 to 0.5, % by weight, based in each case on thepropylene copolymer. The grafting reaction can advantageously be carriedout at from 210° to 290° C., in particular from 210° to 280° C., andduring residence times of from 0.5 to 10, in particular from 0.5 to 5,minutes.

The grafting reaction is effected in the presence of from 0.005 to 0.5,preferably from 0.01 to 0.2, in particular from 0.01 to 0.1, % byweight, based on the propylene copolymer (A₁), (A₂) or (A₃), of a freeradical initiator.

The free radical initiators usually used are organic azo compounds ororganic peroxides, the latter preferably being used. Particularlypreferred organic peroxide compounds have half lives at 210° C. of from1 to 30 seconds. Among these compounds, dicumyl peroxide, monocumyltert-butyl peroxide, di-tert-butyl peroxide,2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane and2,5-dimethyl-2,5-di-(tert-butylperoxy)-hex-3-yne are particularlynoteworthy.

The reactors usually used in plastics technology, for example extrudersor Brabender mixers, may be employed for the grafting of the propylenecopolymers (A₁), (A₂) or (A₃) in the presence of the free radicalinitiator. Twin-screw extruders are particularly suitable. In apreferred embodiment, the propylene copolymer is metered together withthe monomer to be grafted and the free radical initiator into the feedof the twin-screw extruder, where the mixture is first melted at fromabout 120° to 180° C. and grafting is then effected at from 200° to 350°C. for from 0.5 to 5 minutes. The monomer to be grafted is preferablyadded in the liquid state, said monomer being heated beforehand. Themonomer to be grafted may also be introduced into the extruder after themelting of the propylene copolymer. The free radical initiator isusually added either as such or as a solution in an inert hydrocarbon.Advantageously, traces of unconverted monomers to be grafted are removedafter the end of the grafting reaction, in two devolatilization zonesdownstream of the feed zone of the extruder.

The grafted propylene copolymers obtainable in this manner usuallycontain from 0.01 to 1% by weight of the monomer to be grafted. Theyhave good performance characteristics, in particular high adhesivestrength and tensile strength relative to polar substances, for exampleto metals or polyamides. Moreover, they exhibit an improved graftingyield. They are colorless and odorless and have only low residualmonomer contents. Their melt flow indices are from 0.1 to 100,preferably from 1.0 to 50, g/10 min, measured in each case according toDIN 53 735 at 230° C. and 2.16 kg. The melt flow index corresponds tothe amount of polymer which is forced, in the course of 10 minutes at230° C. and under a weight of 2.16 kg, out of the test apparatusstandardized according to DIN 53 735.

The novel, grafted propylene copolymers are suitable, inter alia, asadhesion promoters, films, fibers and moldings. They may also be reactedwith organic crosslinking agents, for example diamines, to givecrosslinked or crosslinkable propylene copolymers.

EXAMPLES

Examples 1 to 6 and Comparative Examples A to F were carried out in aZSK 40 twin-screw extruder from Werner & Pfleiderer. The propylenecopolymers used were introduced into the twin-screw extruder in the formof coarse particles or granules and were melted there at 180° C. Thepolymer throughput in the extruder was 20 kg/h and the average residencetime was 2 minutes.

Example 1

100 parts by weight of a propylene/ethylene copolymer (A₂), consistingof 55.2% by weight of a random ethylene/propylene copolymer (determinedby extraction fractionation according to W. Holtrup, Makromol. Chem. 178(1977), 2335) containing 2.5% by weight of polymerized ethylene(determined by Fourier transform spectroscopy) and 44.8% by weight of apropylene/ethylene copolymer having an ethylene content of 60% by weightand a melt flow index of 1.0 g/10 min (at 230° C. and 2.16 kg, accordingto DIN 53 735) were melted at 180° C. in a ZSK 40twin-screw extrudertogether with 0.02 part by weight of2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane, 0.25 part by weight ofliquid maleic anhydride was added and the mixture was reacted at 260° C.The pressure was 12 bar. After the end of the reaction, unconvertedmaleic anhydride was removed from the polymer melt via adevolatilization zone, and the product was then cooled in a water bath,granulated and dried. The content of grafted maleic anydride, thegrafting yield (content of grafted maleic anhydride based on the totalamount of maleic anhydride used) and the melt flow index of the examplesand of the comparative examples are shown in the table below. The tablealso shows the tensile strength of a glass fiber-reinforced propylenehomopolymer to which 4% by weight of the propylene copolymer graftedwith maleic anhydride have been added.

Comparative Example A

100 parts by weight of the propylene/ethylene copolymer used in Example1 were grafted with 0.25 part by weight of maleic anhydride under theconditions of Example 1 but without the addition of peroxide.

Example 2

Under the conditions of Example 1, 100 parts by weight of apropylene/ethylene copolymer (A₂), consisting of 53.5% by weight of arandom ethylene/propylene copolymer (determined by extractionfractionation according to W. Holtrup, Makromol. Chem. 178 (1977), 2335)containing 2.5% by weight of polymerized ethylene (determined by Fouriertransform spectroscopy) and 44.8% by weight of a propylene/ethylenecopolymer having an ethylene content of 32% by weight and a melt flowindex of 1.0 g/10 min (at 230° C. and 2.16 kg, according to DIN 53 735)were melted together with 0.03 part by weight of2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane at 180° C. in a ZSK 40twin-screw extruder, 0.35 part by weight of liquid maleic anhydride wasadded and the mixture was reacted at 260° C.

Comparative Example B

100 parts by weight of the propylene/ethylene copolymer used in Example1 were grafted with 0.35 part by weight of maleic anhydride under theconditions of Example 1 but without the addition of peroxide.

                  TABLE                                                           ______________________________________                                                                Comparative                                                         Examples  Examples                                                            1     2       A       B                                         ______________________________________                                        Content of grafted maleic                                                                     0.23    0.30    0.19  0.25                                    anhydride (parts by weight                                                    per 100 parts by weight of                                                    propylene copolymer)                                                          Grafting yield (%)                                                                            92      86      76    71                                      Melt flow index*                                                                              3.8     2.2     4.5   2.4                                     (230° C./2.16 kg)                                                      Tensile strength**                                                                            74      76      68    70                                      (MPa)                                                                         ______________________________________                                        *according to DIN 53 735                                                      **according to DIN EN 61:                                                     Matrix:                                                                       96%  by weight of                                                                             homopolypropylene,                                            4%   by weight of                                                                             polypropylene grafted with                                                    maleic anhydride                                              Filler:                                                                       30%  by weight of                                                                             glass fibers                                              

Example 3

100 parts by weight of a propylene/ethylene copolymer (A₁) having a meltflow index of 2 g/10 min (230° C., 2.16 kg, according to DIN 53 735) andcontaining 2.5% by weight of polymerized ethylene (determined by Fouriertransform spectroscopy) were melted together with 0.02 part by weight of2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane at 180° C. in a ZSK 40twin-screw extruder, 0.25 part by weight of liquid maleic anhydride wasadded and the mixture was reacted at 260° C. The pressure was 12 bar.After the end of the reaction, unconverted maleic anhydride was removedfrom the polymer melt via a devolatilization zone, and the product wasthen cooled in a water bath, granulated and dried.

The content of grafted maleic anhydride, the grafting yield (content ofgrafted maleic anhydride, based on the total amount of maleic anhydrideused) and the melt flow index of the examples and of the comparativeexamples are shown in the table below. The table also shows the tensilestrength of a glass fiber-reinforced homopolypropylene to which 4% byweight of the propylene copolymer grafted with maleic anhydride havebeen added.

Comparative Example C

100 parts by weight of the propylene/ethylene copolymer (A₁) used inExample 3 were grafted with 0.25 part by weight of maleic anhydrideunder the conditions of Example 3 but without the addition of peroxide.

Example 4

Under the conditions of Example 3, 100 parts by weight of thepropylene/ethylene copolymer (A₁) used in Example 3 were melted with0.025 part by weight of 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane at180° C. and reacted with 0.30 part by weight of liquid maleic anhydride.

Comparative Example D

100 parts by weight of the propylene/ethylene copolymer (A₁) used inExample 3 were grafted with 0.30 part by weight of maleic anhydrideunder the conditions of Example 3 but without the addition of peroxide.

                  TABLE                                                           ______________________________________                                                                Comparative                                                         Examples  Examples                                                            3     4       C       D                                         ______________________________________                                        Content of grafted maleic                                                                     0.19    0.22    0.12  0.13                                    anhydride (parts by weight                                                    per 100 parts by weight of                                                    propylene copolymer)                                                          Grafting yield (%)                                                                            76      73      48    43                                      Melt flow index*                                                                              5.5     6.2     3.8   3.6                                     (230° C./2.16 kg)                                                      Tensile strength**                                                                            72      73      65    65                                      (MPa)                                                                         ______________________________________                                        *according to DIN 53 735                                                      **according to DIN EN 61:                                                     Matrix:                                                                       96%  by weight of                                                                             homopolypropylene,                                            4%   by weight of                                                                             polypropylene grafted with                                                    maleic anhydride                                              Filler:                                                                       30%  by weight of                                                                             glass fibers                                              

Example 5

100 parts by weight of a propylene/ethylene copolymer (A₃), consistingof 55.2% by weight of a propylene homopolymer (determined by extractionfractionation according to W. Holtrup, Makromol. Chem. 178 (1977), 2335)and 44.8% by weight of a propylene/ethylene copolymer having an ethylenecontent of 50% by weight and a melt flow index of 2.1 g/10 min (at 230°C. and 2.16 kg, according to DIN 53 735) were melted together with 0.02part by weight of 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane at 180°C. in a ZSK 40 twin-screw extruder, 0.25 part by weight of liquid maleicanhydride was added and the mixture was reacted at 260° C. The pressurewas 12 bar. After the end of the reaction, unconverted maleic anhydridewas removed from the polymer melt via a devolatilization zone, and theproduct was then cooled in a water bath, granulated and dried. Thecontent of grafted maleic anhydride, the grafting yield (content ofgrafted maleic anhydride based on the total amount of maleic anhydrideused) and the melt flow index of the examples and of the comparativeexamples are shown in the table below. The table also shows the tensilestrength of a glass fiber-reinforced propylene homopolymer to which 4%by weight of the propylene copolymer grafted with maleic anhydride havebeen added.

Comparative Example E

100 parts by weight of the propylene/ethylene copolymer used in Example5 were grafted with 0.25 part by weight of maleic anhydride under theconditions of Example 5 but without the addition of peroxide.

Example 6

Under the conditions of Example 5, 100 parts by weight of apropylene/ethylene copolymer, consisting of 55.2% by weight of apropylene homopolymer (determined by extraction fractionation accordingto W. Holtrup, Makromol. Chem. 178 (1977), 2335) and 44.8% by weight ofa propylene/ethylene copolymer having an ethylene content of 50% byweight (determined by Fourier transform spectroscopy) and a melt flowindex of 1.0 g/10 min (at 230° C. and 2.16 kg, according to DIN 53 735),were melted together with 0.03 part by weight of2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane at 180° C. in a ZSK 40twin-screw extruder, 0.35 part by weight of liquid maleic anhydride wasadded and the mixture was reacted at 260° C.

Comparative Example F

100 parts by weight of the propylene/ethylene copolymer used in Example5 were grafted with 0.35 part by weight of maleic anhydride under theconditions of Example 5 but without the addition of peroxide.

                  TABLE                                                           ______________________________________                                                                Comparative                                                         Examples  Examples                                                            5     6       E       F                                         ______________________________________                                        Content of grafted maleic                                                                     0.22    0.29    0.18  0.21                                    anhydride (parts by weight                                                    per 100 parts by weight of                                                    propylene copolymer)                                                          Grafting yield (%)                                                                            86      83      72    60                                      Melt flow index*                                                                              5.8     6.2     3.9   3.8                                     (230° C./2.16 kg)                                                      Tensile strength**                                                                            73      75      67    68                                      (MPa)                                                                         ______________________________________                                        *according to DIN 53 735                                                      **according to DIN EN 61:                                                     Matrix:                                                                       96%  by weight of                                                                             homopolypropylene,                                            4%   by weight of                                                                             polypropylene grafted with                                                    maleic anhydride                                              Filler:                                                                       30%  by weight of                                                                             glass fibers                                              

The novel propylene copolymers grafted with free radical initiatorsexhibit in particular an increased grafting yield and a high tensilestrength.

We claim:
 1. A propylene copolymer grafted with α,β-ethylenicallyunsaturated carboxylic acids or carboxylic acid derivatives andconsisting ofa₂) a propylene copolymer (A₂) comprising a randompropylene copolymer (I) containing from 0.1 to 15% by weight ofpolymerized C₂ -C₁₀ -1-alkenes and a random propylene copolymer (II)containing from 15 to 80% by weight of polymerized C₂ -C₁₀-1-alkenesobtained by reacting the monomer to be grafted with thepropylene copolymer (A₂) at from 1 to 300 bar, from 0.01 to 0.35% byweight of the monomer to be grafted, where both stated concentrationsare based on the propylene copolymer, being added to the moltenpropylene copolymer in the presence of from 0.005 to 0.5% by weight of afree radical initiator and the grafting reaction being carried out atfrom 200° to 350° C.
 2. A grafted propylene copolymer as defined inclaim 1, wherein the propylene copolymer (A₂) consists of from 25 to 97%by weight of the random propylene copolymer (I) and from 3 to 75% byweight of the random propylene copolymer (II).